(1) Field of the Invention
The invention relates generally to a package structure of a light emitting diode (LED) device, and particularly to a chip-on-board (COB)-typed LED package with specific phosphors.
(2) Description of the Prior Art
LEDs are now widely used as illuminators, indicators or displays in many kinds of electronic products or industrial applications. One of the advantages of LEDs is that they consume much less electricity, or energy, as comparing with other traditional lighting devices. This is because that LEDs are known as solid state devices that generate light through a luminescence process. Thus the light generated by LEDs is referred to “cold light”. Besides, another advantage of LEDs is its small size. An LED are provided as a semiconductor chip. Hence, LEDs can meet the size-reducing requirement of modern electronic products, especially the delicate electronic products.
LEDs based on the III-nitride materials system have been developed that can efficiently emit light in a relatively narrow band around a peak wavelength in the blue to UV range of the spectrum. Since blue-UV light has a higher photo energy relative to other colors of visible light, such light generated by III-nitride LED is convenient for converting to those other colors of visible light by coating specific wavelength-converting material, such as a phosphor.
While the LED chip applied in an electronic device, it needs to be packaged in a LED package unit, which comprises electrodes for facilitating follow-up fabrication processes. In the LED package unit, the LED chip is usually sealed with a gel material. And a wavelength-converting material, is usually doped within the gel, is usually utilized to convert light of a first wavelength, which is generated from the LED chip, to light of a second wavelength.
A prior single chip, white-light LED package unit incorporates a yttrium-aluminum garnet (YAG) phosphor. Essentially, the phosphor layer produces white light (the second wavelength) from blue light (the first wavelength). The LED package unit is comprised of a blue-light LED chip that is located on a substrate, which is inside an organic YAG phosphor. The YAG phosphor is generally yellow and includes Y3Al5O12:Ce or/and derivatives. Another prior single chip, white-light LED package unit incorporates a terbium-aluminum garnet (TAG) phosphor includes Tb3Al5O12:Ce or/and derivatives. The TAG phosphor is generally a red and green hybrid phosphor.
Comparatively, the LED package unit incorporating TAG phosphor is difficult to achieve high power because of the material property. The LED package unit incorporating YAG phosphor is capable of generating light at high power, but the primary drawback is that the generated light often referred to a kind of “uncomfortable white”. Accordingly, there are different “whites”, “warm whites” and “cold whites” being the most common description. Scientifically, all chromaticies corresponding to black body spectra making up the Planckian locus are “whites”. The white light generated through the YAG phosphor is hard to adjust its color temperature. Not only uncomfortable to the human eyes, it is even not capable of passing some specific standards, such as the product safety standard of the medical field or the traffic safety field.